I voted "throw it outside somewhere", but that is honestly our last resort.
When we use butter (I use a lot of butter), most of that gets cooked in and disposal isn't an issue.
When we cook bacon, I save the drippings in a container and freeze it for reuse. I'll use it in place of butter for making eggs, sauteing vegetables, etc. It gets used up pretty quick without having to waste much that way.
When we fry with oil, I let it cool and then save it in a used oil jug. I can get 2-4 more uses out of it with frying (depending on the application). I also use it to lube the grill prior to cooking out there. When the oil has given up all it's got to give, that's when I throw it out in a corner of the backyard somewhere.